Mbh 12.38.2a

"Vaisampayana continued, 'Then Vyasa, O monarch, that foremost of all persons conversant with the Vedas, casting his eyes upon that ancient and all-knowing person, viz., Narada, said, "If, O king, thou wishest to hear of duties and morality in full, then ask Bhishma, O mighty-armed one, that old grandsire of the Kurus. Conversant with all duties and possessed of universal knowledge, that son of Bhagirathi will remove all the doubts in thy heart on the difficult subject of duties. That goddess, viz., the genius of the celestial river of three courses brought him forth. He saw with his physical eyes all the gods with Indra at their head. Having gratified with his dutiful services the celestial Rishis having Vrihaspati at their head, he acquired a knowledge of the duties of kings. That foremost one among the Kurus obtained a knowledge also of that science, with its interpretations, with Usanas and that regenerate one who is the preceptor of the celestials know. Having practised rigid vows, that mighty-armed one acquired a knowledge of all the Vedas and their branches, from Vasishtha and from Chyavana of Bhrigu's race. In olden days he studied under the eldest-born son of the Grandsire himself, viz., Sanatkumara of blazing splendour, well conversant with the truths of mental and spiritual science. He learnt the duties in full of the Yatis from the lips of Markandeya. The bull among men obtained all weapons from Rama and Sakra. Although born among human beings, his death itself is still under his own control. Although childless, yet he has many regions of bliss hereafter as heard by us. Regenerate Rishis of great merit were always his courtiers. There is nothing among objects that should be known that is unknown to him. Conversant with all duties and acquainted with all the subtle truths of morality, even he will discourse to thee upon duty and morality. Go unto him before he abandons his life breath."